Synaptic Transmission: Neuron Communication

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Questions and Answers

Given the intricate interplay of presynaptic and postsynaptic elements in chemical synapses, how would a targeted disruption of the reuptake mechanisms for neurotransmitters at the presynaptic terminal most directly impact postsynaptic signal transduction?

  • It would result in a perpetual hyperpolarization of the postsynaptic membrane, preventing the initiation of action potentials.
  • It would lead to a complete cessation of neurotransmitter release from the presynaptic neuron due to feedback inhibition.
  • It would selectively enhance the amplitude of inhibitory postsynaptic potentials (IPSPs) while diminishing excitatory postsynaptic potentials (EPSPs).
  • It would cause a transient potentiation followed by a rapid desensitization of postsynaptic receptors due to prolonged agonist exposure. (correct)

Considering the diverse roles of chemical signaling in neuronal communication, what would be the most immediate consequence of a genetic mutation that selectively impairs the synthesis of synaptotagmin within presynaptic neurons?

  • Complete abolition of action potential propagation along the axon.
  • Impaired clustering of voltage-gated calcium channels at the presynaptic active zone.
  • Selective elimination of postsynaptic receptors, leading to a silent synapse.
  • Unregulated and spontaneous fusion of synaptic vesicles with the presynaptic membrane, independent of calcium influx. (correct)

In the context of synaptic transmission, how does the spatial arrangement of axodendritic, axosomatic, and axoaxonic synapses dictate the integrative properties of a postsynaptic neuron, assuming each synapse has a distinct effect on the postsynaptic neuron's membrane potential?

  • Axodendritic synapses, being located further from the soma, uniformly exert a greater influence on the neuron's firing threshold due to dendritic amplification.
  • The spatial location of synapses has no bearing on their influence on the neuron, as signal integration is solely dependent on the number of activated receptors and the quantities of bound neurotransmitters.
  • Axosomatic synapses, positioned closer to the axon hillock, have a disproportionately larger impact on the neuron's action potential initiation compared to axodendritic synapses. (correct)
  • Axoaxonic synapses, universally mediating feedforward inhibition, systematically dampen the influence of all other synaptic inputs.

If a novel neurotoxin selectively disrupts the function of acetylcholinesterase (AChE) at cholinergic synapses, what cascade of events would ensue, impacting both the pre- and postsynaptic neurons?

<p>Persistent depolarization of the postsynaptic membrane due to unchecked ACh receptor activation, potentially leading to excitotoxicity. (A)</p> Signup and view all the answers

Considering the intricacies of nicotinic acetylcholine receptors (nAChRs), predict the outcome if a competitive antagonist with exceptionally high affinity and slow dissociation kinetics were introduced at these receptors.

<p>The magnitude and duration of excitatory postsynaptic potentials (EPSPs) would be markedly reduced, leading to a diminished postsynaptic response and overall reduced signal transmission. (C)</p> Signup and view all the answers

Suppose a researcher discovers a novel compound that selectively inhibits the GTPase activity of the Gα subunit in muscarinic acetylcholine receptors (mAChRs). What downstream consequences would be most directly observed?

<p>Persistent activation of the G protein signaling pathway, leading to prolonged modulation of ion channels or enzyme activity. (D)</p> Signup and view all the answers

How would the introduction of a highly potent and selective inhibitor of vesicular acetylcholine transporter (VAChT) into a cholinergic neuron alter synaptic transmission, considering the neuron's capacity to synthesize acetylcholine?

<p>Progressive depletion of acetylcholine stores within synaptic vesicles, leading to a gradual reduction in quantal size and eventual synaptic failure. (A)</p> Signup and view all the answers

Given the spatial constraints and molecular interactions within a synapse, how would a targeted mutation affecting the scaffolding protein at the postsynaptic density (PSD) alter synaptic plasticity and signal transmission?

<p>Disrupted localization and anchoring of neurotransmitter receptors and signaling molecules, leading to impaired synaptic plasticity and altered postsynaptic responses. (D)</p> Signup and view all the answers

If you were to selectively enhance the activity of reuptake transporters for glutamate in the vicinity of excitatory synapses, what direct consequences would you anticipate regarding postsynaptic neuron excitability and synaptic integration?

<p>A general reduction in postsynaptic neuron excitability, leading to diminished signal transmission and impaired synaptic integration. (D)</p> Signup and view all the answers

In the context of inhibitory synapses, how would selective disruption of the chloride gradient across the postsynaptic membrane affect the efficacy of GABAergic neurotransmission?

<p>GABA receptor activation would result in paradoxical depolarization and increased postsynaptic neuron excitability. (C)</p> Signup and view all the answers

Given the complexity of synaptic transmission, how would selectively enhancing the activity of calcium-dependent potassium channels in the presynaptic terminal impact neurotransmitter release probability?

<p>Reduce neurotransmitter release probability by shortening the duration of action potentials and limiting calcium influx. (B)</p> Signup and view all the answers

If a novel drug selectively prevents the endocytosis of synaptic vesicle membranes following neurotransmitter release, what long-term effects would you predict on synaptic transmission efficacy and presynaptic neuron viability?

<p>Progressive depletion of synaptic vesicles, leading to reduced neurotransmitter release and impaired presynaptic neuron function. (D)</p> Signup and view all the answers

Considering the intricate balance of excitation and inhibition in neural circuits, what would happen if a mutation selectively eliminated axoaxonic synapses within a specific brain region?

<p>A localized increase in excitability due to the disruption of both excitatory and inhibitory neurotransmission within specific circuits. (A)</p> Signup and view all the answers

If a synthetic molecule were designed to mimic the structural and functional properties of nerve growth factor (NGF) receptors specifically at cholinergic synapses, what long-term effects would you anticipate on synaptic plasticity and neuronal survival?

<p>Increased cholinergic neuron survival, enhanced synaptic plasticity, and potential neuroprotection within affected circuits. (A)</p> Signup and view all the answers

Given the complexity of metabotropic receptor signaling, how could a constitutively active mutant of adenylyl cyclase (AC) selectively expressed in postsynaptic neurons alter synaptic integration and plasticity?

<p>Enhanced long-term potentiation (LTP) through persistent activation of protein kinase A (PKA) and subsequent modulation of ion channels. (B)</p> Signup and view all the answers

How would the selective introduction of a calcium-impermeable variant of AMPA receptors (GluA2-lacking AMPARs) into postsynaptic neurons affect synaptic plasticity and vulnerability to excitotoxicity?

<p>Increased vulnerability to excitotoxicity due to unchecked calcium influx through GluA2-lacking AMPARs during periods of heightened synaptic activity. (B)</p> Signup and view all the answers

If a novel genetic therapy introduced a dominant-negative mutation in the gene encoding for synapsin, a protein involved in synaptic vesicle trafficking and release, what would be the most immediate effect on synaptic transmission?

<p>Reduced neurotransmitter release caused by a decrease in the readily releasable pool (RRP) of synaptic vesicles. (A)</p> Signup and view all the answers

How would a genetically-induced reduction in the expression of the postsynaptic cell adhesion molecule (CAM) neuroligin affect synaptic function and circuit formation, given neuroligin's role in binding presynaptic neurexins?

<p>Disrupted synaptic stabilization, leading to reduced synapse number, altered synaptic transmission, and impaired circuit formation. (B)</p> Signup and view all the answers

If a research team developed a light-activated molecule that directly inhibits the activity of the enzyme responsible for synthesizing choline, a precursor for acetylcholine, how would this tool affect cholinergic neurotransmission in real-time upon light exposure?

<p>A rapid and reversible decrease in acetylcholine synthesis, leading to a reduction in synaptic transmission at cholinergic synapses. (B)</p> Signup and view all the answers

Considering the complexities of synaptic integration, predict how the simultaneous activation of both muscarinic and nicotinic acetylcholine receptors on the same postsynaptic neuron would affect its overall excitability and firing pattern.

<p>The neuron would exhibit complex firing patterns due to the interplay of fast (nicotinic) and slow (muscarinic) conductances, potentially leading to either enhanced or suppressed excitability depending on the precise timing and amplitude of receptor activation. (B)</p> Signup and view all the answers

Flashcards

Chemical Synapse

Neurons communicate with other neurons, muscle, or gland cells through chemical signaling involving neurotransmitter release.

Axodendritic Synapse

The synapse that associates with the dendrite of a second neuron.

Axosomatic Synapse

The synapse that associates with the soma/cell body of a second neuron.

Axoaxonic Synapse

The synapse that associates with an axon of a second neuron.

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Synaptic Cleft

The space between the presynaptic and postsynaptic neurons, about 30-50nm wide.

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Synaptic Delay

Delay due to calcium-dependent synaptic vesicle fusion, typically 0.5-5msec.

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Cholinergic Synapse

A mode of chemical signaling in interneurons and efferent neurons of the peripheral nervous system.

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Nicotinic Cholinergic Receptor

A receptor with 2 binding sites for acetylcholine, triggering sodium influx and membrane depolarization.

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Muscarinic Cholinergic Receptor

A receptor that activates a G-protein, leading to opening/closing of ion channels or enzyme activation/inactivation.

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Excitatory Synapse

A synapse that induces a response in the postsynaptic cell, leading to depolarization and bringing it closer to threshold.

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Inhibitory Synapse

A synapse that induces hyperpolarization in the postsynaptic cell, moving it further from threshold potential.

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Study Notes

Synaptic Transmission Overview

  • Chemical synapses are a key aspect of the transmission process.
  • Synaptic communication involves postsynaptic receptors.

Chemical Synapses: Neuron-to-Neuron Communication

  • Neurons use chemical signals for communication with other neurons, muscle cells, or gland cells.
  • This communication occurs through the release of neurotransmitters.

Neurotransmitter Action

  • Neurotransmitters bind to receptors on a second cell.
  • Binding triggers an electrical signal within the postsynaptic cell, continuing the communication.

Types of Presynaptic-Postsynaptic Interactions

  • Axodendritic synapses associate with the dendrites of a second neuron.
  • Axosomatic synapses associate with the soma or cell body of a second neuron.
  • Axoaxonic synapses associate with the axon of a second neuron.

Anatomy of a Synapse at Rest

  • The synaptic cleft refers to the space between the presynaptic and postsynaptic neurons.
  • The distance of the synaptic cleft is 30-50nm
  • Signal transmission is unidirectional, from the presynaptic to the postsynaptic neuron.
  • The presynaptic cell contains neurotransmitters that is a chemical message.
  • Neurotransmitters are stored in membrane-bound vesicles known as synaptic vesicles.

Anatomy of a Synapse: Active

  • The process begins when an action potential arrives at the axon terminal.
  • Voltage-gated calcium channels open, allowing calcium ions to enter the cell.
  • Calcium influx leads to synaptic vesicle membrane fusion and neurotransmitter release.
  • Released neurotransmitters then bind to receptors on the postsynaptic cell, triggering an intracellular response.
  • The time from the action potential reaching the axon terminal to the intracellular response in the postsynaptic cell takes 0.5-5msec.
  • The delay is called synaptic delay and is due to the calcium-dependent synaptic vesicle fusion step.
  • Neurotransmitter activity is reduced through degradation by enzymes on the postsynaptic cell, re-uptake by the presynaptic cell, or diffusion out of the synaptic cleft.

Cholinergic Synapse Communication

  • Cholinergic synapses are a mode of chemical signaling.
  • It is in interneurons and efferent neurons within the peripheral nervous system.
  • Neurons can synthesize Acetyl CoA from lipids, carbohydrates, and proteins through a catabolic reaction.
  • Neurons cannot synthesize choline so it is actively taken up from interstitial fluid.
  • Acetyl-CoA and Choline are converted to Acetylcholine.
  • Acetylcholine is then transported and stored in synaptic vesicles.

Cholinergic Synapse Process

  • Released acetylcholine binds to cholinergic receptors or is degraded by acetylcholinesterase.
  • The degradation of acetylcholine produces choline and acetate.
  • Choline can then be transported back into the presynaptic cell for reuse.

Cholinergic Receptor Types

  • There are two main types of cholinergic receptors: muscarinic and nicotinic,
  • Both bind to acetylcholine but produce differing outcomes.

Nicotinic Cholinergic Receptor

  • Has 2 binding sites for acetylcholine, functioning as a ligand-gated ion channel.
  • Opening of the channel promotes movement of sodium and potassium ions, with sodium movement being greater than potassium movement.
  • The greater movement of sodium ions leads to a depolarization of the membrane potential.
  • It triggers a fast and excitatory response.
  • Nicotinic receptors are found on cells within the peripheral nervous system, like skeletal muscle.

Muscarinic Cholinergic Receptor

  • Acetylcholine binding activates a heterotrimeric G-protein.
  • The GTP-bound alpha subunit then triggers the opening or closing of an ion channel
  • It leads to the activation or inactivation of an enzyme.
  • Muscarinic receptors have a slow response and can be either inhibitory or excitatory.
  • Muscarinic receptors are found in the CNS and in target cells of the autonomic nervous system.
  • Examples include cardiac and smooth muscle, as well as endo/exocrine glands.

Excitatory Synapse

  • Induces a response in the postsynaptic cell that leads to a depolarization of the membrane potential.
  • Depolarization brings the cell closer to the threshold potential.
  • Entry of sodium ions occurs through an ion channel.

Inhibitory Synapse

  • Induces a response in the postsynaptic cell that leads to hyperpolarization of the membrane potential.
  • Hyperpolarization moves the cell further away from the resting or threshold potential.
  • Exit of potassium ions occurs through an ion channel.

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